Italian Ryegrass (Lolium perenne ssp. multiflorum) is a monocot weed in the Poaceae family. In Brazil this weed first evolved multiple resistance (to 2 herbicide sites of action) in 2016 and infests Wheat. Multiple resistance has evolved to herbicides in the Groups A/1, and B/2. These particular biotypes are known to have resistance to clethodim, and iodosulfuron-methyl-sodium and they may be cross-resistant to other herbicides in the Groups A/1, and B/2.

The 'Group' letters/numbers that you see throughout this web site refer to the classification of herbicides by their site of action. To see a full list of herbicides and HRAC herbicide classifications click here.

Greenhouse, and Laboratory trials comparing a known susceptible Italian Ryegrass biotype with this Italian Ryegrass biotype have been used to confirm resistance. For further information on the tests conducted please contact the local weed scientists that provided this information.

Genetics

Genetic studies on Group A, B/1, 2 resistant Italian Ryegrass have not been reported to the site. There may be a note below or an article discussing the genetics of this biotype in the Fact Sheets and Other Literature

Mechanism of Resistance

The mechanism of resistance for this biotype is either unknown or has not been entered in the database. If you know anything about the mechanism of resistance for this biotype then please update the database.

Relative Fitness

There is no record of differences in fitness or competitiveness of these resistant biotypes when compared to that of normal susceptible biotypes. If you have any information pertaining to the fitness of multiple resistant Italian Ryegrass from Brazil please update the database.

The Herbicide Resistance Action Committee, The Weed Science Society of America, and weed scientists in Brazil have been instrumental in providing you this information. Particular thanks is given to Dirceu Agostinetto, Jonas Rodrigo Henckes, Maicon Fernando Schmitz, and Leandro Vargas for providing detailed information.

Recently, the acetohydroxyacid synthase
(AHAS) amino acid substitution Asp376Glu was detected
in a Lolium perenne population originating in France. This
is the first documented occurrence of the Asp376Glu single-
nucleotide polymorphism in a Lolium species. The
effects on herbicide efficacy and plant fitness are presented.
Separation of the original population into different genetic
subgroups allowed the comparison of different L. perenne
AHAS genotypes according to their susceptibility to
AHAS-inhibiting herbicides. Root and shoot biomass
accumulation as well as tiller production was analysed for
resistant and sensitive populations. Genotype-specific
AHAS activity and inhibition were studied in vitro, using
recombinant Arabidopsis thaliana DNA. Plants expressing
the AHAS Asp376Glu genotype were resistant against
mesosulfuron ? iodosulfuron, pyroxsulam and propoxycarbazone.
To imazamox, reduced susceptibility for dosages
below 140 g a.i. ha-1 was observed. In the absence of
herbicide, no significant impact of the Asp376Glu genotype
on shoot biomass and tiller accumulation could be
observed, whereas root biomass of the Asp376Glu genotype
was significantly reduced by 68 % compared to the
AHAS genetic wild type. The AHAS enzyme study
revealed reduced AHAS enzyme rate of 48 % for the
Asp376Glu genotype compared to the AHAS genetic wild
type. This study highlights the role of the amino acid
exchange on resistance profile against the most relevant
AHAS-inhibiting herbicides. First indications were found
that fitness of the Asp376Glu genotype is hampered..

Plants were obtained from two populations of Italian ryegrass (Lolium multiflorum) and three populations of perennial ryegrass (Lolium perenne) from different vineyards in Marlborough and Nelson that were suspected of being resistant to glyphosate following many consecutive applications of this herbicide over recent years. Each population was multiplied by splitting out tillers, and this was also done for plants taken from a population of each species from Manawatu pastures where they had not been exposed to glyphosate application. A dose-response experiment showed that four populations taken from the vineyards were about 10 times as resistant to glyphosate as those plants that had not been previously exposed to the herbicide. The experiment was repeated and showed one perennial ryegrass population to have a 30-fold level of resistance. These are the first confirmed cases of glyphosate resistance within New Zealand..

Lolium perenne ssp. multiflorum (Italian ryegrass) is a major weed problem in wheat production. Being an obligate outcrossing species, it has a high propensity to evolve resistance to herbicides. This study was conducted to determine the level of resistance and resistance patterns of Italian ryegrass populations in the United States to ACCase- (diclofop and pinoxaden) and ALS (imazamox, mesosulfuron, and pyroxsulam) inhibitors. Dose-response bioassays were conducted on 47 populations from suspect herbicide-resistant fields in the southern United States (Arkansas, Mississippi, Georgia, North Carolina, South Carolina, Virginia), Kansas, and Washington collected between 2008 and 2011 from fields suspected of resistance to ALS inhibitors. Eighty-seven percent of the populations were resistant to diclofop. Eight of the diclofop-resistant populations (25%) were also resistant to pinoxaden. Thirty-eight diclofop-resistant populations (81%) were resistant to at least one ALS inhibitor. Thirty-nine populations (83%) were resistant to mesosulfuron, 38 of which were also resistant to pyroxsulam. All mesosulfuron-resistant populations tested were cross-resistant to imazamox and pyroxsulam. Cross-resistance patterns to ALS inhibitors differed. Of 45 populations with resistance to ACCase or ALS inhibitors, 35 (78%) had multiple resistance to both modes of action. The majority of diclofop-resistant L. perenne populations can be controlled with pinoxaden, but widespread resistance to pinoxaden can evolve soon if it is intensively used. A comprehensive weed management approach prior to planting will be critical in managing L. perenne in wheat and preventing or delaying resistance evolution..

Insect pest and weeds are two major problems for forage and turf grasses. In this study, scarab larvae- and herbicideresistant transgenic perennial ryegrass (Lolium perenne L.) was obtained by transforming it with cry and bar genes simultaneously via the Agrobacterium-mediated method. To optimize the callus induction and plant regeneration conditions, various concentrations of 2,4-dichlorophenoxyacetic acid and 6-benzylaminopurine were assayed. The transformation efficiencies of different Agrobacterium suspension media, used during Agrobacterium-mediated transformation, were compared. Then, plasmids of pCAMBIA3301 containing cry gene (cry8Ca2 or cry8Ga) and bar gene, driven by ubiquitin promoter, were transformed into perennial ryegrass. The transformants were generated and confirmed by both Southern hybridization analysis and Western hybridization analysis. Further, the resistance of transgenic perennial ryegrass plants to scarab larvae and herbicide were analyzed. After 30 d of co-cultivation with scarab larvae, the damage to the root system of transgenic plants was less than that of non-transgenic control plants. Additionally, the leaves of transgenic plants were resistant to Basta®, while leaves of the wild plants wilted after Basta® spraying. These results show that cry gene and bar gene were successfully transferred into perennial ryegrass by the Agrobactgerium-mediated method, and convey resistance to scarab larvae and herbicide in transgenic perennial ryegrass plants..

Incorporating the use of glyphosate into a weed management program offers turfgrass managers increased flexibility and cost savings when attempting to control troublesome weeds such as annual bluegrass (ABG) (Poa annua L.). Field trials of glyphosate tolerant perennial ryegrass (PRG) (Lolium perenne L.) cultivars, JS501 and Replay, were initiated to determine glyphosate tolerance and rates required for ABG control. In the tolerance trial, glyphosate was applied on 15 Sept. 2010 and 9 Aug. 2011 at rates of 0, 0.29, 0.58, 1.16, 1.74, 2.32, and 3.48 kg.ha-1 a.e. Glufosinate was also applied at 0, 1.68, and 3.37 kg.ha-1 a.i. In the ABG control trial, glyphosate was applied on 17 June followed by 19 Aug. 2009 and 25 June followed by 25 Aug. 2010 at rates of 0, 0.15, 0.29, 0.44, and 0.58 kg.ha-1 a.e. In the tolerance trial, linear regression analysis revealed a glyphosate application rate of 0.81 kg.ha-1 a.e. was required to cause 20% leaf firing. By the end of the trial, the highest rate of glufosinate resulted in nearly complete desiccation of 'Replay' PRG. For ABG control, after four glyphosate applications over a 2-year period, a rate of 0.29 kg.ha-1 a.e. or greater resulted in less than 10% ABG. Untreated plots had ~83% ABG infestation. Discoloration was not noted for either PRG cultivar at any point over the 2-year trial period. Based on the environmental conditions of each trial, results suggest a recommended application rate should be 0.29 kg.ha-1 a.e. during summer months. This rate is sufficient for ABG control and also provides protection in case spray overlap occurs during an application..